Effect of type of primary processing on the microstructure, CTE and mechanical properties of magnesium/alumina nanocomposites

Magnesium based composites containing 2.5 wt.% of nano-sized Al₂O₃ (50 nm) particulates reinforcement were synthesized using an innovative disintegrated melt deposition technique and blend-press-sinter powder metallurgy technique followed by hot extrusion. Microstructural characterization of the materials revealed uniform distribution of reinforcement, grain refinement and the presence of minimal porosity. Properties characterization revealed that the presence of nano-Al₂O₃ particulates led to an increase in dimensional stability, hardness, elastic modulus, 0.2% yield strength, UTS and ductility of pure magnesium. Amongst the composites, the ingot metallurgy processed material exhibited superior modulus and ductility while powder metallurgy processed material exhibited superior yield strength and ultimate tensile strength. The results further revealed that the overall combination of tensile properties of these materials remained superior when compared to high strength magnesium alloy AZ91 reinforced with much higher weight percentage of SiC. Fractography studies revealed that the typical brittle fracture of pure magnesium changed to ductile due to the incorporation of nano-Al₂O₃ particulates. An attempt is made in the present study to correlate the effect of nano-sized Al₂ O₃ particulates as reinforcement and processing type with the microstructural and tensile properties of magnesium.